Pre-mixed batches of dialysis solution supplied from an open tank by gravity head pressure to a number of artificial kidneys in large clinics have largely been replaced by systems designed to make up and supply dialysis solution only as needed by each individual artificial kidney. Dialysis concentrate and water are mixed in a venturi device in the direct supply line to a dialysis storage tank in U.S. Pat. No. 3,528,550. In U.S. Pat. Nos. 3,515,275 and 3,920,556 the use of positive displacement piston pumps in continuous dialysis solution supply systems for hemodialysis are disclosed.
Frequently, dialysis fluid for hemodialyzers is supplied by forming a mixture of a concentrated solution of dialysis chemicals from a reservoir with water in the ratio of approximately one part of concentrate to 34 parts water by volume. Proportioning devices must be capabIe of maintaining this concentration within prescribed limits for the duration of the hemodiaylsis treatment, which is on the order of 6 to 14 hours. Existing proportioning means utilized in dialysis solution delivery systems often utilize positive displacement mechanical devices, such as pistons or rotary pumps, in which separate pumps of different volumetric capacities are used to supply the concentrate and the water. These pumps are expensive, experience failures of moving seals, are mechanically complex and are subject to corrosion and salt deposit due in part to the highly concentrated solution.
It is often desirable to have large volumes of dialysis solution prepared for use by several patients. To prevent microbial contamination and caramelization of dextrose, the solution should not be stored for long periods of time.
Shipments of concentrated solutions of chemicals which are later diluted in proportioning systems are relatively expensive since a large volume of water must be shipped for each pound of dry chemical. Concentrated dialysis solutions may also experience undesirable precipitation of the chemicals. Thus, it is desirable for larger institutions to prepare their own dialysis solution from drums of dry chemicals using their own water supply.